Experimental study on the diffusion–kinetics interaction in heterogeneous reaction of coal

• DOI: 10.1007/s10973-017-6386-1
• Publication Date: 2017-04-18T05:48:31Z
• Authors: Zeyang Song; Xinyan Huang; Minggang Luo; Junhui Gong; Xuhai Pan
• Keywords: 13. Climate action; 0211 other engineering and technologies; 0202 electrical engineering, electronic engineering, information engineering; 02 engineering and technology; 7. Clean energy

The diffusion of oxygen (O2) plays an important role in the heterogeneous oxidation of coal and biomass, but is inadequately understood. This work aims to study the influence of intra-, inter-particle and external O2 diffusions on the high-temperature heterogeneous oxidation using the TG-FTIR technique and two bituminous coals as example. Results show that coal sample of higher reactivity and smaller pore surface area is more sensitive to the O2 diffusion. Specifically, increasing the size of particle, the reduced intra-particle (Knudsen) diffusion can reduce the conversion rate by 10–50%. While increasing the size of sample, the effective inter-particle diffusion shows a linear decrease. Comparatively, the influences of inter-particle and external diffusion in the TG scale ( 10 mg) and low heating rates (2 K min−1), the influence of thermal diffusion is strong enough to cause a thermal leap for the oxidation. Kinetic analysis using nth-order model-fitting method predicts the apparent activation energy (E) decreases with increasing reactivity. However, both model-free and Kissinger’s methods show E increases with increasing reactivity, against the physical definition of E. This work may help understand the diffusion–kinetics interaction in the fuel conversion and smoldering fire of coal and biomass.